The present invention relates to a fiber-composite material that can be used as an ultra-high-heat-resistant structural material, and a highly lubricated and wear resistant material, and more particularly to a method of preparing the fiber-composite material.
The development of space-round-trip aircraft and space planes in the space development field, high-temperature burning gas turbines in the energy field, and high-temperature gas furnaces and fusion reactors in the atomic energy field have experienced rapid development recently.
As an energy source next to nuclear energy and solar energy, application of hydrogen energy has been researched. In this process, expensive metals and fine ceramics have been examined as vessels for the reactions. High strength and high reliability (toughness, shock resistance) materials at medium or high temperatures (200 to 2000xc2x0 C.), and durability that is not affected by the environment (corrosion resistance, oxidation resistance, radiation resistance) are demanded on these structural elements.
Today, as to ceramic materials having excellent heat resistance, silicon nitride and silicon carbide materials are being developed as new ceramics. However, these materials have a defect of brittleness as their intrinsic property, and they are extremely fragile if cracked and are also susceptible to thermal and mechanical shock.
As means for overcoming these defects inherent in ceramics, a ceramics-based composite material (CMC) that is combined with continuous ceramics-based fiber has been developed. Because the material has high strength and high toughness even at high temperature, and has excellent shock resistance and excellent durability against various environments, the research and development on the material is actively being done as the main ultra-high heat-resistant structural material chiefly in Europe and the USA.
For example, several hundred to several thousand pieces of long ceramic fibers having a diameter of about 10 xcexcm are bundled to form fiber bundles (yarn), and the fiber bundles are arranged two or three dimensionally to form one-direction sheets (UJD sheet) or various kinds of cloths. These sheets or cloths are laminated to make a preformed product with a predetermined shape (fiber preform). To make a matrix within the preformed product by the CVI method (Chemical Vapor Infiltration: Chemical-vapor impregnating method) or by the inorganic- polymer-impregnation burning method, ceramic powder is filled into the above-mentioned preformed product by casting-molding method and then is sintered to make a matrix. Thus, ceramics-based fiber-composite material (CMC) that is combined with fibers in a ceramic matrix has been developed.
As specific examples of CMC, C/C composite and SiC fiber-reinforced Sixe2x80x94SiC composite are known. The former is produced by forming a matrix made of carbon in the gap among carbon fibers arranged in two-or three-dimensional directions, and the latter is produced by impregnating Si into the molded product comprising SiC fibers and SiC particles.
In British Patent Specification No. 1457757, the processing method of impregnating C/C composite with melting Si is disclosed. According to the method, the composite material that is a C/C composite impregnated with Si is supposed to be produced.
C/C composite has been employed in a wide scope of fields because of its excellent shock resistance owing to its high toughness, of its lightness and its excellent strength, but the composite has a limitation in being used as ultra-high heat-resistant structural material, because the composite cannot be used at high temperature in the presence of oxygen since the composite is composed of carbon. Further, the composite has a defect of low abrasion resistance when used as sliding elements because of its rather low hardness and low compression strength.
On the other hand, SiC fiber-reinforced Sixe2x80x94SiC composite is excellent in oxidation resistance, creep resistance and in spalling resistance, but the composite is easily scratched. Also, the SiC fiber has a problem that the fiber cannot be used as such structural material as a turbine blade that has a complex shape or a thin section, because of the low shock resistance of the fiber. The Sic fiber is inferior in lubricating property compared to Sixe2x80x94SiC or the like, and the drawing effect between the body material and fiber is small, which leads to the inferior toughness compared to C/C composite.
In the composite material described in the British Patent Specification No. 1457757, which is a C/C composite impregnated with Si, the common C/C composite that has been known is used, and the composite material has the structure that has a lot of fine pores in the whole body. That is, as described in Example 1 of the British Patent Specification No. 1457757, after carbon fiber is coated with phenol resin, the fiber is arranged in a mold, compressed and cured so that the desired fiber direction and shape are obtained, and then the obtained molded product is released from the mold and is heated at 800 to 900xc2x0 C. in nitrogen atmosphere to carbonize the phenol resin. Thus, C/C composite, having the structure in which the fiber is orientated in one direction and in which the fiber is laminated, is obtained.
In such C/C composite, the phenol resin is carbonized to become a part of the carbon matrix, but because the rate of carbonization is about 50%, the C/C composite has a structure having a lot of fine pores in the whole body. When this C/C composite is dipped in melting Si to impregnate Si, although the vicinity of the surface thereof is permeated with Si, it is impossible to make Si permeate into the whole C/C composite, especially into the center part homogeneously. Therefore, the C/C composite has still the defect that is characteristic of the C/C composite material and that has not yet been solved.
In addition, when the C/C composite having such structure is impregnated with Si, the structure of carbon fiber near the surface is broken because of being directly contacted with high temperature melted Si. As a result, there arises a problem that the C/C composite loses its shock resistance, strength, high lubricant property and wear resistance.
The present invention has been made to solve the above-mentioned problem, and an object of the present invention is to provide a composite material having excellent shock resistance, corrosion resistance in strong oxidation and corrosion environments, creep resistance, spalling resistance, wear resistance, low friction coefficient, further, lightness and strength. Additionally, the present invention has a self-restorative ability by which a defect is healed under a certain condition.
The present invention provides a fiber-composite material comprising: a yarn aggregate in which yarn including at least a bundle of carbon fiber and a carbon component other than carbon fiber is three-dimensionally combined and integrally formed without separation from each other; and a matrix made of Sixe2x80x94SiC-based material filled between the yarn adjacent to each other within the yarn aggregate.
In the present invention, preferably, the matrix has a silicon carbide phase having grown along the surface of the yarn, the matrix has the silicon phase comprising silicon, and more preferably, the silicon carbide phase has grown between the silicon phase and the yarn.
The matrix may have an inclined composition in which the content rate of silicon becomes higher at increasing distances from the surface of the yarn. Preferably, the yarn aggregate includes a plurality of yarn array elements, each of the yarn elements is formed by arranging the plurality of yarns in a substantially parallel direction and two dimensionally, and each of the yarn array elements is laminated to form the yarn aggregate. Then, preferably, the yarn array elements adjacent to each other are structured such that the longitudinal direction of each yarn intersects with each other.
In the present invention, the matrices are connected to each other within the fiber-composite material to form a three-dimensional network structure. More specifically, the matrices are arranged in a substantially parallel direction and two-dimensionally within each of the yarn array elements, and the matrices having grown within each of the yarn array elements adjacent to each other are connected to each other, to thereby form a three-dimensional lattice of the matrices.
According to the present invention, there is provided a method of preparing fiber-composite material, comprising the steps of: producing bundles of carbon fiber by impregnating a component of powdery carbon and a component of organic binder into the bundles of carbon fiber, which eventually forms a matrix shape; forming a plastic coat around the bundles of carbon fiber to obtain an intermediate material; molding the intermediate material to obtain a molded product by making the intermediate material into a yarn-shape; then, forming the intermediate material into a sheet if circumstances require; and laminating a predetermined amount of the material, or burning the molded product to obtain a burned product; holding the molded product or the burned product and Si, at 1100 to 1400xc2x0 C. in an atmosphere of inert gas; and heating the molded product or the burned product and Si to a temperature from 1450 to 2500xc2x0 C., to thereby impregnate Sixe2x80x94SiC-based material into the inside of pores of the molded product or the burned product.
In the method, preferably, the molded product or the burned product and Si are held at a temperature of from 1100 to 1400xc2x0 C. under a pressure of 0.1 to 10 hPa for one or more hours, and an inert gas is controlled to flow in an amount of 0.1 or more normal litters (NL) per 1 kg of the total weight of the molded product or the burned product and Si. Preferably, the molded product or the burned product and Si are heated to a temperature of from 1450 to 2500xc2x0 C. under a pressure of 0.1 to 10